In the quadratic equation ax² + bx + c = 0, the value of b² - 4ac is the discriminant—the same numbers and letters that are under the square root sign of the quadratic formula. This is actually the products of the squares of the polynomial root differences. In other words, this quantity characterizes certain properties of the quantity’s roots. The discriminant is often used for such mathematical concepts as metrics, modules, quadratic fields, and polynomials.